fix: ctrl+p print dialog, gallery 400 error, poll multi-choice UX

- Suppress Ctrl+P browser print dialog via SuppressPrintShortcut in
  ClientNonUIFeatures (no UI opened, just preventDefault)
- mxcUrlToHttp: build URL manually instead of delegating to SDK.
  The SDK forces allow_redirect=true when useAuthentication=true;
  Synapse's /_matrix/client/v1/media/thumbnail rejects that with 400.
  Manual construction omits allow_redirect entirely.
- Gallery: redesign using folds color tokens (color.Surface.*) instead
  of non-existent CSS custom properties; add ThumbState so broken
  images show an icon placeholder; use useAuthentication for thumbnails
  now that the URL builder is fixed; "Load More" always visible.
- PollCreator: replace raw <button> with folds Button components so the
  Single/Multiple choice toggle renders with actual visual difference.
- PollContent: support multiple-choice polls end-to-end —
  myVote:string → myVotes:Set<string>; computeVotes collects all
  m.selections (not just [0]); toggle-select for multi, radio for
  single; checkbox/radio indicator icons next to each option;
  "◉ Poll · Multiple choice" / "Single choice" label in header;
  sends full selections array on every vote event.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/app/features/room/PollCreator.tsx

@@ -1,6 +1,6 @@
 import React, { useState } from 'react';
 import { Room } from 'matrix-js-sdk';
-import { Box, Icon, IconButton, Icons, Text, config } from 'folds';
+import { Box, Button, Icon, IconButton, Icons, Text, config } from 'folds';
 import { useMatrixClient } from '../../hooks/useMatrixClient';
 
 interface PollCreatorProps {
@@ -193,34 +193,26 @@ export function PollCreator({ roomId, onClose }: PollCreatorProps) {
           )}
         </div>
 
-        <div style={{ display: 'flex', flexDirection: 'column', gap: config.space.S100 }}>
+        <Box direction="Column" gap="100">
           <Text size="L400">Selection Type</Text>
-          <div style={{ display: 'flex', gap: config.space.S200 }}>
+          <Box gap="200">
             {(['single', 'multiple'] as const).map((type) => {
               const active = type === 'multiple' ? isMultiple : !isMultiple;
               return (
-                <button
+                <Button
                   key={type}
-                  type="button"
+                  size="300"
+                  variant="Primary"
+                  fill={active ? 'Solid' : 'None'}
+                  radii="300"
                   onClick={() => setIsMultiple(type === 'multiple')}
-                  style={{
-                    padding: `${config.space.S100} ${config.space.S300}`,
-                    borderRadius: config.radii.R300,
-                    border: `1px solid ${active ? 'var(--bg-primary-main)' : 'var(--bg-surface-border)'}`,
-                    background: active ? 'var(--bg-primary-main)' : 'transparent',
-                    color: active ? 'var(--tc-primary-on-primary)' : 'var(--tc-surface-high)',
-                    cursor: 'pointer',
-                    fontSize: '13px',
-                    fontWeight: active ? 600 : 400,
-                    transition: 'all 0.15s ease',
-                  }}
                 >
-                  {type === 'single' ? 'Single choice' : 'Multiple choice'}
-                </button>
+                  <Text size="B300">{type === 'single' ? 'Single choice' : 'Multiple choice'}</Text>
+                </Button>
               );
             })}
-          </div>
-        </div>
+          </Box>
+        </Box>
 
         {error && (
           <Text size="T200" style={{ color: 'var(--tc-danger-normal)' }}>
@@ -229,38 +221,27 @@ export function PollCreator({ roomId, onClose }: PollCreatorProps) {
         )}
 
         <Box direction="Row" justifyContent="End" gap="200">
-          <button
-            type="button"
+          <Button
+            size="400"
+            variant="Secondary"
+            fill="Soft"
+            radii="300"
             onClick={onClose}
-            style={{
-              background: 'var(--bg-surface-low)',
-              border: '1px solid var(--bg-surface-border)',
-              borderRadius: config.radii.R300,
-              padding: `${config.space.S200} ${config.space.S400}`,
-              cursor: 'pointer',
-              color: 'var(--tc-surface-high)',
-              fontSize: '14px',
-            }}
-          >
-            Cancel
-          </button>
-          <button
             type="button"
-            onClick={handleSubmit}
-            disabled={submitting}
-            style={{
-              background: 'var(--bg-primary-main)',
-              border: 'none',
-              borderRadius: config.radii.R300,
-              padding: `${config.space.S200} ${config.space.S400}`,
-              cursor: submitting ? 'not-allowed' : 'pointer',
-              color: 'var(--tc-primary-on-primary)',
-              fontSize: '14px',
-              opacity: submitting ? 0.7 : 1,
-            }}
           >
-            {submitting ? 'Creating...' : 'Create Poll'}
-          </button>
+            <Text size="B400">Cancel</Text>
+          </Button>
+          <Button
+            size="400"
+            variant="Primary"
+            fill="Solid"
+            radii="300"
+            onClick={handleSubmit}
+            type="button"
+            disabled={submitting}
+          >
+            <Text size="B400">{submitting ? 'Creating…' : 'Create Poll'}</Text>
+          </Button>
         </Box>
       </div>
     </div>